Can I use the 3.5 MM in Pathfinder with little to no changes? If not what is a way I can update them to Pathfinder? I wanna use classic D&D monsters not present in Pathfinder.
Just remember that their Pathfinder effective CR may differ from 3.5.
For everything else, there's Mastercard.
Pretty much 'quick' conversion involves using a monster exactly as it stands. You know how to run a Spot check in a world that uses Perception. You know how to run Tumble in a world that uses Acrobatics. Look at the monster, find a good CR for it, possibly increase its natural armor to give it an appropriate AC, and voila.
CMB and CMD will need to be calculated on the fly, but they're pretty straight forward. Also, some spell-like abilities may relate to spells that behave differently.
Can I use the 3.5 MM in Pathfinder with little to no changes? If not what is a way I can update them to Pathfinder? I wanna use classic D&D monsters not present in Pathfinder.
Yes you can. But keep in mind that some major changes have occurred for undead, Ghouls in particular. They no longer paralyze for minutes. They paralyze for rounds. Also the undead template no longer gives immunity to cold. Apart from that you should be able to transfer the abilities pretty regularly.
Can I use the 3.5 MM in Pathfinder with little to no changes? If not what is a way I can update them to Pathfinder? I wanna use classic D&D monsters not present in Pathfinder.Yes you can. But keep in mind that some major changes have occurred for undead, Ghouls in particular. They no longer paralyze for minutes. They paralyze for rounds. Also the undead template no longer gives immunity to cold. Apart from that you should be able to transfer the abilities pretty regularly.
It also no longer provides immunity to sneak attacks or crits.
A lot of the monsters that did not make it into the first bestiary made it into bestiary 2 and bestiary 3 also. The monsters are online so you don't have to buy the book.